1. Field of the Invention
The present invention relates to asynchronous Wideband Code Division Multiple Access (WCDMA) communications, and more particularly to a method and apparatus for efficiently determining and transmitting control information required for transmitting Enhanced Uplink Dedicated Channel (EUDCH or E-DCH) data.
2. Description of the Related Art
A Universal Mobile Telecommunication Service (UMTS) system is a 3G (3rd Generation) mobile communication system which is based on Global System for Mobile (GSM) communications (i.e., a European mobile communication system), and uses WCDMA technology. The UMTS system provides consistent services enabling mobile phone and computer users to perform packet-based transmissions of text, digitized voice, video, and multimedia data at a high rate of more than 2 Mbps no matter where in the world they are located. The UMTS system uses a concept called a “virtual connection” which is a packet-switched connection using a packet protocol such as the Internet Protocol (IP), and which is always available to any other end point in the network.
The UMTS system uses an Enhanced Dedicated Channel (E-DCH) to enhance packet transmission performance in uplink communication from User Equipment (UE) to a Node B (also referred to as a base station). The E-DCH, which is enhanced from the general DCH to support more stable high-speed data transmission, is a transport channel supporting technologies such as Adaptive Modulation and Coding (AMC), Hybrid Automatic Retransmission Request (HARQ), and Node B controlled scheduling.
The AMC is a technology for increasing the utilization efficiency of a data channel by adaptively determining different modulation and coding schemes of the data channel according to channel states between a Node B and a UE. The AMC uses Modulation and Coding Scheme (MCS) levels indicating various combinations of modulation and coding schemes. The AMC increases overall channel utilization efficiency by adaptively determining the MCS level according to the channel state between the Node B and the UE.
The HARQ is a technique in which a data packet is retransmitted for error compensation if an error occurs in an initially transmitted data packet. The receiver receives and decodes the retransmitted packet by soft-combining it with the initially received data packet. The HARQ technique can be classified into Chase Combining (CC), in which the same bits as those of the initially transmitted packet are retransmitted when an error occurs in the initially transmitted packet, and Incremental Redundancy (IR) in which different bits from those of the initially transmitted packet are retransmitted when an error occurs in the initially transmitted packet.
The Node B controlled scheduling is a technique used for data transmission using an E-DCH in a system with the E-DCH established. In this technique, a Node B determines a maximum allowed data rate of a UE and determines if the UE is permitted to transmit uplink data, and informs the UE of the determination. Based on the determination information received from the Node B, the UE determines a possible uplink E-DCH data rate. When this technique is used, an MCS level is adaptively determined based on channel states between the UE and the Node B to increase channel utilization efficiency.
FIG. 1 is a conceptual diagram illustrating data transmission through an E-DCH in a radio link.
In FIG. 1, reference numeral 110 denotes a Node B supporting the E-DCH, and reference numerals 101, 102, 103 and 104 are UEs receiving E-DCH signals. The Node B 110 detects channel states of the E-DCHs used by the UEs 101 to 104, and schedules data transmission of each of the UEs. To increase the overall system performance, this scheduling is performed in such a manner that a low data rate is allocated to the UE 104 furthest from the Node B 110, and a high data rate is allocated to the UE 101 near the Node B 110, while preventing a Rise Over Thermal (ROT) value of the Node B 110 from exceeding a target value.
FIG. 2 is a message flow diagram illustrating the procedure for transmission and reception through an E-DCH.
First, at step 203, the Node B 201 and the UE 202 set up an E-DCH therebetween. This setup procedure includes the transmission of messages through a dedicated transport channel. If the E-DCH is set up, the UE 202 notifies the Node B 201 of state information (i.e., scheduling information) at step 204. This state information includes, for example, the amount of data awaiting transmission stored in a buffer, available UE transmit power, and UE transmit power information indicating uplink channel information.
The Node B 201 and receives monitors the state information of the UE 202 at step 211. At step 211, the Node B 201 schedules the UE 202 to perform uplink packet transmission, and transmits scheduling assignment information to the UE 202. The scheduling assignment information includes a data rate, transmission timing, etc.
Using the scheduling allocation information, the UE 202 determines, at step 212, a Transport Format (TF) of an E-DCH for transmission in the uplink, and transmits the determined TF information to the Node B at step 206 and also transmits uplink (UL) data to the Node B at step 207 through the E-DCH. The TF information includes a Transport Format Resource Indicator (TFRI) that indicates information required to demodulate the E-DCH. The UE 202 performs the uplink data transmission of step 207 based on an MCS level selected according to the channel state and the data rate allocated by the Node B 201.
At step 213, the Node B 201 determines if an error exists in the data and the TFRI received from the UE 202. At step 208, the Node B 201 transmits Non-Acknowledgement (NACK) information to the UE 202 through an ACK/NACK channel if an error exists, and transmits Acknowledgement (ACK) information to the UE 202 through an ACK/NACK channel if no error exists. If the ACK information is transmitted to the UE 202, the data transmission is completed, so that the UE 202 transmits new user data to the Node B 201 through the E-DCH. On the other hand, if the NACK information is transmitted to the UE 202, the UE 202 retransmits data containing the same contents as transmitted at step 207 to the Node B 201 through the E-DCH.
Since the UE uses a different MCS level in each transmission through the E-DCH, and uses different Spreading Factors (SFs) according to the size of data to transmit, the Node B must normally acquire control information (i.e., TFRI) of packets of uplink data to normally demodulate the uplink data.
The TFRI information required to demodulate the uplink data includes a Modulation Format (MF), a Spreading Factor (SF), and a Transport Block Size (TBS) of the uplink data. The E-DCH transmission employs modulation formats such as Binary Phase Shift Keying (BPSK), Quadrature PSK (QPSK) and 8-ray PSK (8-PSK) because it is very important to decrease Peak to Average power Ratio (PAR) in the E-DCH transmission. The E-DCH transmission can use a variety of Orthogonal Variable Spreading Factors (OVSF) in the uplink because there is no limitation on the use of code resources in the uplink. The E-DCH transmission provides a peak data rate of 2 Mbps, and supports various TBSs to provide various services.